Pest Expert Overview: Sawtoothed Grain Beetles in Bryan & College Station
Sawtoothed grain beetles are among the most common insects found in stored food products. Despite their name, they are not limited to grain and can infest a wide variety of foods stored in kitchens, pantries, warehouses, grocery stores, pet food areas, and commercial food facilities.
Adult sawtoothed grain beetles are very small, measuring approximately 1/10 inch long. They are slender, flattened, and reddish-brown to nearly black. Their flattened bodies allow them to crawl through tiny gaps in food packaging and hide in narrow cracks around pantry shelves.
The sawtoothed grain beetle, Oryzaephilus surinamensis, is in the Order Coleoptera and the Family Silvanidae.
The common name comes from the six tooth like projections located along each side of the thorax directly behind the head. These projections are easily visible under magnification but may be difficult for homeowners to see without a hand lens.
Sawtoothed grain beetles are usually brought into a home inside an already infested food product. They do not normally enter from outdoors and then search the pantry for food.
Identifying Sawtoothed Grain Beetles
Sawtoothed grain beetles have narrow, flattened bodies with parallel sides. The head is visible from above, and the antennae end in a small club.
The six saw-like projections on each side of the thorax are the most distinctive identifying feature.
Sawtoothed grain beetles are nearly identical to merchant grain beetles, Oryzaephilus mercator. The two species were once considered the same insect and can be difficult to separate without magnification.
Merchant grain beetles generally have larger eyes and a slightly different head shape. Merchant grain beetles can also fly, while sawtoothed grain beetles cannot.
The two species have similar feeding habits and are controlled using the same basic methods inside homes. Finding the infested product is much more important than separating two nearly identical beetles.
Life Cycle
Sawtoothed grain beetles undergo complete metamorphosis and develop through four stages: egg, larva, pupa, and adult.
Adult females deposit tiny white eggs loosely inside food products or in cracks near a food source. Unlike grain weevils, they do not place their eggs inside whole kernels.
The eggs hatch into small, slender larvae that are yellowish-white with brown heads. The larvae crawl freely through the food and feed as they develop.
When fully grown, the larvae usually attach themselves to a solid surface or construct a crude pupal cell from small food particles. Pupation may occur inside the food, along package seams, in shelf cracks, or beneath loose debris.
Adults emerge and continue feeding in the same product or crawl into nearby packages.
Development can be completed in approximately one month under warm, favorable conditions. Cooler temperatures or poor quality food can extend development considerably.
Adult sawtoothed grain beetles may live for several months. Because both the larvae and adults feed, an overlooked product can support a continuing infestation for a long time.
What Do Sawtoothed Grain Beetles Eat?
Sawtoothed grain beetles feed on a broad range of dry food products.
Commonly infested products include:
- Flour and cornmeal
- Breakfast cereal
- Oatmeal
- Pasta
- Crackers and cookies
- Rice
- Bread crumbs
- Cake and baking mixes
- Nuts and seeds
- Dried fruit
- Chocolate and candy
- Spices
- Dry pet food
- Pet treats
- Bird seed
- Rodent bait
- Dried meat products
Sawtoothed grain beetles are secondary stored product pests. They usually cannot successfully develop inside hard, undamaged grain kernels.
Instead, they feed on cracked grain, processed foods, grain damaged during handling, or kernels previously attacked by grain weevils and other primary pests.
Adult beetles may occasionally enter damaged whole kernels, but the presence of sawtoothed grain beetles generally directs an inspection toward processed foods, broken grain, food dust, and spilled products.
Why They are Pests
Sawtoothed grain beetles do not sting, damage clothing, or feed on the structure of a home. Their importance comes from their ability to contaminate stored food.
Both larvae and adults feed within food products. They leave behind feces, shed skins, insect fragments, eggs, and dead insects.
Heavy infestations can give food an unpleasant odor or flavor. The activity of large numbers of insects may also increase moisture within a product and contribute to mold growth.
Their flattened bodies allow them to enter packages through extremely small openings. They may crawl beneath folded cardboard seams, around loose fitting lids, or through tiny imperfections in paper and plastic packaging.
Some infestations begin before the product is purchased. Others spread after beetles emerge from one package and crawl into surrounding foods.
Because sawtoothed grain beetles cannot fly, adults found around a home reached those locations by crawling. Their presence on countertops, walls, windowsills, or in rooms away from the pantry usually means they dispersed from an infested product somewhere inside the building.
Sawtoothed Grain Beetle Prevention and Control
The most important step in controlling sawtoothed grain beetles is locating and removing the infested food.
Spraying the beetles seen crawling around a kitchen may kill those individuals, but it will not eliminate the eggs, larvae, pupae, and adults inside food packages.
Inspect all susceptible products in the pantry and nearby cabinets. Look for:
- Living adult beetles
- Small yellowish larvae
- Shed skins
- Insect fragments
- Powdery food debris
- Holes or damage in packaging
- Beetles caught along package seams
- Unusual odors or clumping
Do not limit the inspection to products made from whole grain. Sawtoothed grain beetles are commonly found in processed foods such as cereal, pasta, crackers, flour, baking mixes, nuts, and dried fruit.
Inspect products that are used infrequently and have been stored for a long time. Old spices, forgotten baking supplies, partially used bags of nuts, and boxes pushed to the back of a pantry are common sources.
Pet food, bird seed, pet treats, and rodent bait should also be inspected. Large bags stored in garages, closets, or utility rooms can support substantial infestations.
Infested products should be placed inside a sealed bag and removed from the house.
After removing the source:
- Vacuum pantry shelves, corners, cracks, shelf pin holes, and cabinet joints.
- Remove spilled flour, grain, pet food, and other food debris.
- Pull out removable shelves and clean beneath their edges.
- Inspect nearby packages before returning them to the pantry.
- Dispose of the vacuum contents outside.
- Store susceptible foods in tightly sealed glass or heavy plastic containers.
- Avoid keeping old or rarely used dry products indefinitely.
Do not stop inspecting after finding the first infested package. Sawtoothed grain beetles are active crawlers and may have entered several nearby products.
Questionable food can sometimes be frozen to kill developing insects. However, freezing will not remove feces, shed skins, insect fragments, or other contamination already present. Most inexpensive infested foods should simply be discarded.
Heating may also kill stored product insects, but the entire product must reach a lethal temperature. Leaving a package in a hot vehicle, attic, or garage is not a reliable treatment.
Insecticide applications inside food storage cabinets are generally unnecessary. Pesticides should never be applied directly to food, food packaging, or food contact surfaces unless the label specifically permits that use.
Crack and crevice treatments may occasionally be useful in severe commercial infestations, but insecticides do not replace inspection, source removal, and sanitation.
The treatment that solves the problem is finding where the beetles are developing.
It is normal to see occasional adults for a short time after the infested product has been removed. Beetles that had already left the food may continue crawling through the home.
Continued or increasing activity usually means that another infested product or accumulation of food debris has been overlooked.
Preventing Sawtoothed Grain Beetles
Inspect dry food products before purchasing them whenever possible. Avoid packages that are damaged, torn, leaking food dust, or have insects visible inside.
Once products are brought home:
- Transfer flour, cereal, rice, pasta, nuts, and similar foods into sealed containers.
- Clean spilled food promptly.
- Wash and dry storage containers before refilling them.
- Do not add new food to a container that still contains an older product.
- Purchase quantities that can be used within a reasonable amount of time.
- Rotate stored products so older food is used first.
- Inspect pet food and bird seed before placing it into storage.
Sealed containers may not prevent an infestation that was already inside a product when purchased. However, they will contain emerging beetles and prevent them from spreading into surrounding foods.
Professional Sawtoothed Grain Beetle Control
Sawtoothed grain beetle infestations can be difficult to locate because the insects feed on such a wide variety of products and can crawl through extremely small spaces.
The source may be an obvious bag of flour or cereal, but it may also be spices, nuts, pet food, bird seed, rodent bait, or food debris beneath shelving.
A professional inspection can help confirm the identification, distinguish sawtoothed grain beetles from similar pantry pests, locate overlooked food sources, and determine whether the infestation has spread into multiple products.
If you are dealing with an infestation of sawtoothed grain beetles, Venus Pest Company can help. Founded by Aggie Entomologist Dr. Scott Lingren, we provide expert, eco-friendly Integrated Pest Management solutions in Bryan and College Station. To get started, fill out the contact form, call/text 979.774.0486 or email [email protected]. Don’t let nuisance pests take over your home!
